Design of the Power Supply for Alfvén Eigenmodes Excitation on J-TEXT

The Alfvén eigenmodes (AEs) excitation system has been designed and installed on the J-TEXT tokamak. The system consists of a series resonant power supply and an excitation antenna. Under the typical operating conditions of the J-TEXT, the excitation frequency is thought to be in the range of 200-700 kHz. In order to match the AEs frequency, the external excitation system needs to scan its frequency automatically in experiments. In the implementation process, the whole frequency band is divided into several segments. For each one of them, the resonant circuit matches different capacitors. Specifically, the resonant capacitor is arranged in the form of a fixed capacitor in parallel with a variable capacitor. In the last campaign, a 2.3-nF fixed capacitor and a 1-nF variable capacitor are picked up, so that the resonant capacitance could change from 2.3 to 3.3 nF. In addition, the matching units were applied to optimize the antenna currents. Finally, the formal plasma discharge experiments have been carried out on the J-TEXT. The results show that the excitation frequency can be changed from 445 to 510 kHz in 350 ms, and the output current is able to reach 50 A. This paper is focused on the design of the excitation system, particularly the strategy of frequency scanning.